you do not need a permit just to own a gun. only to carry one in public.
criminals dont care about having a permit and just carry anyway. what's an extra weapons charge when you are going to murder a dozen people?
on another note, there is a bit of mystery involving the circumstances of this event. im not going to go full blown "the govt did it!!" conspiracy theory, but some things are peculiar.
this was an unemployed med student. yet he had tens of thousands of dollars worth of swat/military equipment and body armor. stuff that is not only expensive, but pretty difficult to obtain as a civilian. in addition to the bombs in his apartment. seems someone else was funding this. and he didnt set off any red flags with purchases, despite stock piling like 10,000 rounds of various types of ammo. probably purchased over time. this wasnt a fluke "heat of the moment" type shooting. it was planned and calculated.
also, why go through the trouble of booby trapping your whole apartment with bombs, and then tell cops about it? something just seems weird here.
and then talks about this happening so close to the UN Arms treaty stuff. some are speculating they may be trying to advocate to effectively revoke our 2nd amendment rights. (which i doubt, just passing along the info)